1. Field of the Invention
The present design relates generally to the art of circular polarizing eyewear, and more specifically to enhanced techniques for cardboard, paper, plastic-framed or other kinds of eyewear that can lower the cost of providing circular polarizing eyewear for viewing projected stereoscopic motion pictures and maintaining the highest image quality.
2. Description of the Related Art
Circular polarized light for image selection has been the subject of several prior disclosures. Reference is made to the work of Land, U.S. Pat. No. 2,099,694, and Walworth in the proceedings of the SPIE, Vol. 462, Optics in Entertainment, “Three-Dimensional projection with Circular Polarizers.” Certain companies, including REAL D, the assignee of the present invention, project or release stereoscopic motion pictures in the theatrical cinema using circular polarization for image selection. Previously, for the most part, linear polarization has been used for image selection and not circular polarization. Part of the reason for this lack of acceptance has been the high cost of circular sheet polarizer materials compared with the more widely used linear sheet polarizer.
Stereoscopic movies using polarization employ one of two projection methods. The first uses two projectors, either digital or film projectors, with plastic sheet polarizers in front of the lens of each projector. Such an arrangement projects onto a so-called “silver screen,” actually a screen that has been coated with aluminum pigment or paint to conserve polarization. The second is gaining in popularity and uses a single digital projector for the field-sequential approach for projecting stereoscopic movies as described by Lipton et al in U.S. Pat. No. 4,792,850, and first manufactured by StereoGraphics Corp. and further described by Lipton in “The Stereoscopic Cinema: From Film to Digital Projection,” SMPTE Journal, September 2001. For either the single or dual projector method, a “silver screen” is employed and audience members wear eyewear having sheet polarizing filters.
A major commercial problem with regard to circular polarizing material has to do with cost rather than performance. A circular polarizer comprises a linear polarizer and a quarter-wave retarder. These materials are often made in different factories, and this means that a manufacturer of circular polarizer may purchase the raw lens materials from two factories, both receiving a profit for producing the individual items. The manufacturer of the circular polarizer, who combines or laminates the polarizer and retarder sheets, also profits for the construction of each device. In some cases the device passes through a supplier or reseller, so there are many entities deriving profits from the sale of such devices, increasing the overall cost of the circular polarizer materials.
Linear polarizers cost considerably less than circular polarizers and find favor with many exhibitors for this reason alone. However, performance of linear polarizers is inferior for various reasons, including the Law of Malus, discussed below. One virtue of using the linear polarization scheme for image selection is that it is possible to deploy inexpensive eyewear that can be disposed after a single use. Alternatively, exhibitors such as theme parks often use plastic-framed eyewear that can be cleaned and reused. In most circumstances, theme parks have the infrastructure and financial capability to recycle eyewear but theatrical cinema exhibitors do not. Therefore, some type of high performance and low cost disposable eyewear for use in neighborhood cinemas and multiplexes is desirable. Moreover, recycled eyewear frequently become warped and scratched after on several cleanings.
Circularly polarized low cost eyewear has previously employed sheets of polarizing and retarder materials laminated together. However, the costs involved include obtaining the polarizer material, obtaining the retarder material, laminating the polarizer material with the retarder material, and including the laminated polarizer and retarder material in the finished eyewear. Each of these steps or processes takes time and money to complete.
In addition, the business model that is used for theatrical release requires that the exhibitors charge as much as twice the studio's cost of the eyewear for the studio to recover its costs. Therefore, in order to encourage the distribution of stereoscopic movies, a lowest overall production cost for eyewear is mandatory.
Eyewear designs having relatively low manufacturing and distribution costs that enable high quality image viewing in both single and dual projector methods can provide significant advantages over eyewear designs previously made available. Such eyewear designs could provide the ability for theater owners to effectively and efficiently provide eyewear to audiences for enhanced viewing experiences as compared against eyewear previously available.